1970 GMC Truck Conventional Models Series 4500-6500 Sales Brochure. If you want the best truck features modern engineering can provide, you want a GMC medium! Build more over-the-road profit over more years with GMC mediums. Tough GMC chassis smooth the way for safe cargo delivery. GMC combines two-fisted engines with single-minded economy. Engine chart on inside back cover. Specifications on back. Good condition with minor wear [see photos].